The plant biodiversity of the Wadi Allaqi Biosphere Reserve (Egypt): impact of Lake Nasser on a desert wadi ecosystem

A data set comprising 95 stands of desert vegetation, collected from the Wadi Allaqi Biosphere Reserve and its environs within the South-Eastern Desert of Egypt during 1985–90, was analysed using multivariate procedures (two-way indicator species analysis: TWINSPAN; detrended correspondence analysis: DCA; canonical correspondence analysis: CCA), to produce a classification of plant communities in the area, and to examine the relationships of these plant communities to natural and man-induced features of the physical environment of the area (in particular, the influence of Lake Nasser, a major impoundment of the River Nile formed in 1964). The vegetation classification produced groupings broader, in both floristic and ecological terms, than those found by earlier studies of this area. In total 78 plant species were recorded from four phytogeographic elements. Four principal vegetation groups were identified, of which one is new to the area, and is the result of major environmental changes affecting the downstream part of the Wadi Allaqi system, following periodic flooding of the wadi by Lake Nasser during the past 30 years. This community was indicated by Tamarix nilotica. There was a strongly-zoned (downstream–upstream) pattern to the vegetation within this lower part of Wadi Allaqi, which appears to be a function of the probability of flooding by the lake. The remaining three vegetation groups occur higher in the wadi basin. Groundwater-dependence appeared to be important in defining a group indicated by Acacia tortilis, as well as the Tamarix nilotica group. The two remaining groups, characterized respectively by Acacia ehrenbergiana and Cullen plicatum, represent vegetation groups which are precipitation-dependent, and which tolerate drier conditions within the Allaqi system.